Accelerating Effect of Copper Ion on the Reactivation of Reduced Taka-amylase A through Catalysis of the Oxidation of Sulfhydryl Groups*

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Abstract
Reduction of all the disulfide bonds in Taka-amylase A by mercaptoethanol in 8 M urea yields randomly coiled polypeptide chain. Intact structure of the enzyme can be recovered by removal of the reducing and denaturing reagents and by subsequent air-oxidation. When the reoxidation mixture was free from contamination, the reoxidation and reactivation proceeded very slowly. These changes were found to be markedly accelerated by the addition of some of transition metal ions which have been well known with thiols of small molecular weight to catalyze the oxidation of sulihydryl groups by molecular oxygen. Among them, copper ion was the most effective. A mechanism of the catalysis was proposed. Reoxidation of reduced proteins so far reported are presumed to be catalyzed by the contaminating metal ions, since no catalyst has been used. To obtain reproducible results in reoxidation expriments, the amount of the catalyst should be strictly controlled.